MANAGING ECOLOGICAL FLOWS IN TROPICAL MONTANE STREAMS

Water diversions and the development of small and large hydropower dams are occurring at an unprecedented rate in most montane tropical environments. This development is also causing conflicts between onsite and off-site users of aquatic resources and has greatly increased the need and demand for managing instream flows. While the need to establish environmental and instream flow allocations is widely recognized, calculating the actual flow regimes needed to maintain ecological and hydrologic functions is a complex task. This is particular true in tropical montane streams that have relatively frequent high discharge events, high sediment loads and supply limited transport systems, complex morphology, and diadromous fauna which require a migration between fresh and salt waters. This paper reviews the current state of instream flow analysis for montane tropical streams in the Caribbean and Central America. Examples of several recent instream flow analysis are discussed in relation to the geomorphology and habitat of these streams. In addition, recent mitigation efforts including offsite dams and stream-bed water intakes are discussed and compared.